1. Field of the Invention
The present invention relates to new types of copolyimides and a process for the. preparation thereof for use in films, insulating coatings, molding products, and the like due to their excellent thermal stabilities and mechanical and electrical properties.
2. Description of the Prior Art
Various types of polyimides are known in the art. The polyimides exhibit excellent thermal stabilities and mechanical properties. The polyimides, however, have high glass transition temperatures so that they exhibit problems with respect to processability. In order to improve the processabilities of the polyimides, they are manufactured from aromatic diamines containing "flexible hinges". However, most of these polyimides have decreased thermal stabilities.
In order to improve the properties of such prior art polyimides through copolymerization method, processes for the preparations of random copolyimides are known in the art, wherein one aromatic dianhydride and at least two aromatic diamines or one aromatic diamine and at least two aromatic dianhydrides are used However, such processes require caution in each step since such copolymers can change their properties depending on the copolymerization conditions.